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Exploring Hot Dense Matter at RHIC and LHC Peter Jacobs Lawrence Berkeley National Laboratory Lecture 3: Collective Flow and Hydrodynamics 6/22/11 Hot Matter at RHIC and LHC - Lecture 3 1 “Hydrodynamic” flow in unusual systems 1. Cornstarch+water (“oobleck”, Non-Newtonian fluid) on an audio speaker: http://youtu.be/3zoTKXXNQIU 2. Stream of sand particles striking a target in symmetric geometry: http://nagelgroup.uchicago.edu/Nagel-Group/Granular.html 6/22/11 Hot Matter at RHIC and LHC - Lecture 3 2 Elliptic flow of a degenerate Fermi fluid J. Thomas et al., Duke time Optically trapped atoms degenerate Fermi gas nanokelvin temperature (!) Interactions magnetically tuned to Feshbach resonance infinite 2-body scattering cross-section prototypical“strongly-coupled” system Prepare the system with spatial anisotropy and let it evolve develops momentum anisotropy elliptic flow” (!) 6/22/11 Hot Matter at RHIC and LHC - Lecture 3 3 What is fluid dynamics? Fluid dynamics = Conservation of Energy+Momentum for long wavelength modes of excitation breaks down for small or dilute systems Degrees of freedom for a relativistic fluid • fluid velocity um (4-vector) • pressure p (scalar) • energy density e (scalar) • General relativity: metric tensor gmn Quantum field theory: • Energy-Momentum Tensor: Tmn • Conservation of Energy+Momentum: 6/22/11 Hot Matter at RHIC and LHC - Lecture 3 4 Shear viscosity in fluids Shear viscosity characterizes the efficiency of momentum transport quasi-particle interaction cross section Comparing relativistic fluids: h/s • s = entropy density • scaling param. h/s emerges from relativistic hydro eqns. • generalization for non-rel. fluids: h/w (w=enthalpy) (Liao and Koch, Phys.Rev. C81 (2010) 014902) 6/22/11 Large s small h/s Strongly-coupled matter ”perfect liquid” Hot Matter at RHIC and LHC - Lecture 3 5 Gauge/string duality and the QGP AdS/CFT correspondence (Maldacena ’97): conjecture of deep connection in String Theory between strongly coupled non-abelian gauge theories and weak gravity near a (higher-dimensional) black hole AdS/CFT correspondence = holography 6/22/11 Hot Matter at RHIC and LHC - Lecture 3 6 Shear viscosity and entropy in String Theory (AdS/CFT) h/s of a black hole (M. Natsuume, hep-ph/0700120) Shear visc. ~ cross section: h lim s BH Area 0 Beckenstein entropy: S BH Area kB 4G h ~ 0.1 s 4k B Universal result: gauge theory plasmas with gravity duals have a universal low value h/s=1/4 at strong (‘t Hooft) coupling Kovtun, Son and Starinets (KSS), PRL 94, 111601 (More precisely: h/s=1/4 is only Leading Order result for infinite coupling) 7 6/22/11 Hot Matter at RHIC and LHC - Lecture 3 Back to nuclear collisions… STAR 6/22/11 Hot Matter at RHIC and LHC - Lecture 3 8 Collective Flow of QCD Matter Initial spatial anisotropy Final momentum anisotropy py px z y y 2 x 2 y 2 x 2 x Interaction of constituents v2 p x2 p y2 p x2 p y2 Elliptic flow 6/22/11 Hot Matter at RHIC and LHC - Lecture 3 9 A teaser: v2 at RHIC v2 is sizable: ~10% anisotropy mT Light particles mn 0 shear viscosityh 0 Heavy particles Mass hierarchy vs momentum is characteristic of common velocity distribution Ideal hydro: qualitative agreement but missing the details 10 6/22/11 Hot Matter at RHIC and LHC - Lecture 3 How do we actually measure v2? STAR Heavy Ion event: Find momentum-weighted plane of azimuthal view in symmetry of the event momentum space (“reaction plane” ΨR ) py px z y x p x2 p y2 Calculate the momentum-weighted v2 2 azimuthal asymmetry relative to that plane: p x p y2 6/22/11 Hot Matter at RHIC and LHC - Lecture 3 11 Wait: can it really be that simple? Actually, no. Initial state is (highly) non-uniform: nucleon correlations, local hot spots of energy density,… Theory calculation: Schenke, Jeon, Gale, PRL 106, 042301 This will bias the measurement of the reaction plane orientation: z y x 6/22/11 Hot Matter at RHIC and LHC - Lecture 3 12 Another complication: “non-flow” from jets RHIC/Star Large anisotropic contribution to momentum flow in the event But complex and unknown correlation with reaction plane orientation LHC/CMS z y x 6/22/11 Hot Matter at RHIC and LHC - Lecture 3 13 Controlling “non-flow” Want to remove all correlations that are not due to collective flow of many particles: • Measure reaction plane orientation and flow signal in widely separated regions of phase space (large Dh separation) • Compare cumulants of various order: 2,4,6,…particle • cumulants are well-known in statistics: isolate true nparticle correlations by removing lower order correlations (e.g. n particles can be mutually correlated due to 2-particle correlations) Methods are under good control small systematic uncertainties due to “non-flow” correlations 6/22/11 Hot Matter at RHIC and LHC - Lecture 3 14 Elliptic flow v2: LHC vs RHIC ALICE, PRL 105, 252302 (2010) Striking similarity of pT-differential v2 at RHIC and LHC 6/22/11 Hot Matter at RHIC and LHC - Lecture 3 15 Hydrodynamic modeling of a heavy ion collision P. Romatschke, QM11 Shear viscosity 6/22/11 Bulk viscosity Hot Matter at RHIC and LHC - Lecture 3 16 6/22/11 Hot Matter at RHIC and LHC - Lecture 3 17 6/22/11 Hot Matter at RHIC and LHC - Lecture 3 18 v2: data vs. viscous hydrodynamic modeling Song, Bass, and Heinz, arXiv:1103.2380 pT-differential pT-integrated central peripheral Preferred values: h/s(RHIC)=0.16, h/s(LHC)=0.20 …..???? 6/22/11 Hot Matter at RHIC and LHC - Lecture 3 19 Higher harmonics ALICE arXiv:1105.3865 ALICE: v2 and v3 have contradictory preferences for h/s not understood 6/22/11 Hot Matter at RHIC and LHC - Lecture 3 20 CMS: similar ambiguities Qualitatively: h/s is within ~2-3 times 1/4 Quantitatively: need better theoretical and experimental control for definite measurement 6/22/11 Hot Matter at RHIC and LHC - Lecture 3 21 Shear viscosity: expectations from QCD Analytic: Csernai, Kapusta and McClerran PRL 97, 152303 (2006) Lattice: H. Meyer, PR D76, 101701R (2007) Chiral limit, resonance gas pQCD w/ running coupling 1/4 Lattice QCD Temperature (MeV) 6/22/11 If TLHC > TRHICHot , expect h/s(LHC) > h/s(RHIC) Matter at RHIC and LHC - Lecture 3 22 Remember this plot: QCD calculated on the lattice (mB=0) Slow convergence to non-interacting Steffan-Boltzmann limit What carries energy - complex bound states of q+g? “strongly-coupled” plasma? g DOF T 4 Energy density 30 S. Borsanyi et al., JHEP 1011, 077 (2010) 2 Both flow measurements and Lattice QCD calculations suggest that the Quark-Gluon Plasma at high temperature is very 4 a simple gas of non-interacting quarks and gluons differentTthan Why? What are the dominant degrees of freedom (“quasiparticles”)? We don’t know yet… Cross-over, not sharp phase transition (like ionization of atomic plasma) 6/22/11 Temperature [MeV] Hot Matter at RHIC and LHC - Lecture 3 23